Plastic closures formed from thermoplastic polymeric materials have met with widespread acceptance in the marketplace for use on containers having beverages and like products. Closures of this type, which can be efficiently formed by compression molding or injection molding, are typically configured for threaded application to associated containers, and are further configured to engage and cooperate with the container to effectively seal the container's contents. Closures of this type may be configured as so-called composite closures, including an outer closure cap or shell, and an inner sealing liner, or a so-called “linerless” closure, where the closure cap itself is configured to provide the desired sealing cooperation with the associated container.
While closures of the above type have been very commercially successful, versatile and economic use of these types of closures has been promoted by reducing the amount of polymeric material required for forming each closure, that is, making each closure more lightweight. However, in this regard, certain dimensional considerations become important. In particular, closures of this nature are typically applied to associated containers by high-speed, automatic capping equipment, including capping heads or chucks which rotatably fit each internally threaded closure to an associated, externally threaded container. While weight savings in such closures can be desirably achieved by reducing the thickness of the side wall portion of the closure, it will be appreciated that the use of such automated capping equipment typically requires that the outside diameter of the skirt portion of the closure fall within a certain specified range. In other words, for application to a given configuration of container neck, or “finish”, the outside diameter of this skirt portion is essentially fixed.
As will be appreciated, reducing the weight of a closure by reducing the thickness of the side wall or skirt portion will necessarily result in increased clearance between the inside of the skirt portion, and an associated container finish, given that the outside diameter of the skirt portion is predetermined. However, the increased clearance between the inside surface of the skirt portion and the associated container finish must be accommodated in order to achieve efficient closure application, as well as the desired sealing and performance characteristics for the closure.
An additional consideration relates to enhancing high-speed closure application. High-speed application ordinarily requires that the internal thread formation of the closure mate properly and efficiently with the external thread formation of the associated container. It is particularly desirable to avoid misapplication or “cocked” closures, which can undesirably interrupt the efficient high-speed application.
Currently, closures are applied to containers by rotating the closures until the closure/container thread interactions draw the closure down, causing the seal feature of the closure to contact the extreme upper rim of the container finish. There are occasionally issues where the closure thread does not engage the container thread properly, causing misapplied closures. This is especially the case with containers with more than one thread start. When this occurs, the closure has the tendency to be damaged when application is complete, or by being cocked on the container finish, which can undesirably impair sealing performance.
To address this, the closure threads can be made smaller so that with top loading, the closure thread can more easily jump over the container thread on application, and correct the tendency to cock. However, when this is done, it becomes easier to strip the closure during application, resulting in damaged threads, large variation of application angle, and therefore impairment of sealing performance. Additionally, the smaller closure thread can cause issues in pressurized applications, where the internal pressure within the container can cause the closure thread to jump over the container thread, and cause the closure to be released from the container finish.
The present closure has been particularly configured to minimize the use of polymeric material from which the closure is formed, while at the same time facilitating high-speed application with automatic capping equipment.